Installation for producing a hot-rolled strip

ABSTRACT

The invention relates to a plant for producing a hot strip from a metal melt in accordance with the twin-roll casting process. To increase the melt throughput in the tundish to above the capacity limit of a one-stranded casting plant operating according to the twin-roll casting process and at the same time to reduce the batch casting times significantly with minimal investment and operating costs, the invention proposes a plant configuration in which a casting ladle ( 1 ) with a melt outlet ( 5 ) is assigned a tundish ( 6 ) for receiving the metal melt from the casting ladle ( 1 ), in that this single tundish ( 6 ) is equipped with at least two bottom outlets ( 8   a,    8   b ) for transferring the metal melt to two twin-roll casting devices ( 10   a,    10   b ), in that each casting nip ( 13   a,    13   b ) is assigned at least one of the bottom outlets ( 8   a,    8   b ) of the tundish ( 6 ), and the two casting nips ( 13   a,    13   b ) are arranged at an angle of 15° to 180°, or parallel and offset with respect to one another in terms of their longitudinal extents.

[0001] The invention relates to a plant for producing hot strip from a metal melt in accordance with the twin-roll casting process using two twin-roll casting devices.

[0002] A plant of this type for producing thin, near net shape hot strip, preferably steel strip, in accordance with the twin-roll casting process substantially comprises two driven, oppositely rotating casting rolls which are arranged at a distance from one another and the axes of rotation of which lie in a horizontal plane. They form a casting nip, the lateral boundary of which is formed by side plates pressed onto the casting rolls at the end sides. Side plates which can be pressed vertically onto the casting roll lateral surfaces are also known for this purpose. The two casting rolls and the side plates form a melt space into which metal melt is introduced through a submerged casting nozzle. At the two cooled lateral surfaces of the casting rolls, metal melt solidifies to form strand shells which at the narrowest gap between the casting rolls combine to form a cast strip. The metal strip, which is discharged vertically downward, is then diverted into the horizontal plane, is subjected to further processing steps in downstream treatment devices and is wound into metal coils.

[0003] A plant which uses the twin-roll casting process described is already known from AT-B 406 938. Two twin-roll casting plants arranged parallel next to one another are independently supplied with melt, each twin-roll casting plant being assigned a separate ladle turntable and a separate tundish. The metal strip produced is wound into coils and the coils from the two casting plants are conveyed to a further rolling plant, where they are processed further. This plant arrangement doubles the production capacity.

[0004] In the vertical twin-roll casting process, the strip casting speed is limited to 15 to 150 m/min for a strip thickness of 1.5 to 5 mm by the dissipation of heat, which is limited in terms of time and to a short path length on the casting roll surface. Consequently, the production capacity which can be achieved at a plant of this type is limited to between approx. 0.5 and 1.5 t/min and meter strip width. This corresponds to a maximum production capacity of 100 t/h for a standard one-stranded plant for casting widths of up to 1300 mm.

[0005] In the case of casting ladles with a capacity of 150 t of metal melt and above, as are frequently used, this leads to casting times of more than two hours and therefore to undesirable changes in casting conditions over the course of the casting time.

[0006] In certain continuous casting plants, in particular in casting plants for producing metal strands of low width, such as billet continuous casting plants and bloom casting plants, it is quite normal to minimize the casting time per casting ladle by using a multistranded casting installation. In this case, the permanent molds and the downstream strand-guidance means are arranged closely adjacent. The melt is fed to the individual permanent molds by a common casting ladle via a common tundish through a plurality of casting openings. A plant of this type, in which a multiplicity of billet strands of very small cross section can be produced by means of tubular molds arranged in semicircle form, is already known from DE-A 19 08 648. According to this arrangement of permanent molds, the individual cast strands are removed at identical angular intervals in beam form. With such small cross sections, the problem of arranging two permanent molds for casting strands with strip cross sections and high length/width ratios with a limited tundish size does not arise.

[0007] There are also a few known examples of two-strand strip casting plants (EP-B 347 662, JP-A 62-187505), the permanent molds of which are supplied with melt by a tundish. However, these permanent molds do not operate in accordance with the vertical twin-roll casting process, but rather are equipped with track molds or conventional plate molds, which may if appropriate have a central widened region for the submerged casting nozzle. On account of the lateral roll bearing, the side plates which can be placed onto the end sides of the casting rolls together with their hydraulic actuating mechanism and the drives for the casting rolls, the twin-roll casting plant required for the twin-roll casting process needs much more space in the axial direction than permanent molds of other designs. Given these design conditions and the desired high product width, it is not possible for the casting rolls to be brought so close together in the axial direction that a common tundish for two twin-roll casting plants could be arranged above them in the customary way. There are limits imposed on the dimensions of a tundish on account of the need for uniform heating before it starts to operate and for the desired melt guidance and conditioning in the tundish. Tundishes with a longitudinal extent of more than 10 m are scarcely technically viable, leading to very high volumes of metal and very large wetted refractory lining surface areas in relation to the total throughput of the two twin-roll casting devices and therefore to an increased consumption of refractory material and to yield losses.

[0008] Therefore, it is an object of the invention to avoid these drawbacks and difficulties and to propose a casting plant which operates according to the twin-roll casting process and with which it is possible to significantly increase the melt throughput in the tundish to above the capacity limit of a one-strand casting plant operating in accordance with the twin-roll casting process and, at the same time, to significantly reduce the batch casting times. A further object of the invention is to ensure that the conditions for the metal melt, in particular relating to constancy of casting temperature over the casting time, are met without additional heating and to keep the dimensions of the tundish, in particular the distance between the bottom outlets, small. A further object of the invention is to find a plant configuration in which the maximum number of plant components are used together in a plurality of production lines.

[0009] According to the invention, this object is achieved through the fact that a casting ladle with a melt outlet is assigned a tundish for receiving the metal melt from the casting ladle, that this single tundish is equipped with at least two bottom outlets for transferring the metal melt to two twin-roll casting devices, in that each casting nip is assigned at least one of the bottom outlets of the tundish, and the two casting nips are arranged at an angle α of 15° to 180°, preferably of 45° to 120°, in particular of 60° to 120°, with respect to one another in terms of their longitudinal extents. A favorable arrangement results if the two casting nips are arranged at an angle α of approximately 90° with respect to one another in terms of their longitudinal extents.

[0010] An advantageous plant design is achieved in each twin-roll casting device forms a production line with the strip treatment devices arranged downstream of it and the production lines which are supplied with metal melt from a common tundish are arranged at an angle of 15° to 180°, preferably of 45° to 120°, in particular of 60° to 120°, with respect to one another. The angular position of the two production lines with respect to one another enables them to be brought closer together in the region of the actual twin-roll casting device, and the distance between the central supply positions for the metal melt is minimized, thereby shortening the length of the tundish. A preferred plant arrangement results if the production lines which are supplied with metal melt by a common tundish are arranged at an angle β of approximately 90° with respect to one another.

[0011] It is possible to avoid the need to arrange strip-diverting devices in the production lines if the angle α which [lacuna] the position of the casting nips of the two twin-roll casting devices with respect to one another is equal to the angle β which defines the position of the two production lines with respect to one another.

[0012] Further advantages of the arrangement according to the invention result if common service areas for at least one, preferably at least two, of the following applications are arranged in the smaller angle region between two adjacent twin-roll casting devices and the strip treatment devices arranged downstream of them:

[0013] cast-rolling shops,

[0014] casting roll changeover station,

[0015] roll change station,

[0016] roll grinding mills,

[0017] plant operating stand,

[0018] product logistics.

[0019] Synergistic effects from reduced investment costs and savings in operation and during maintenance also result in the case of other plant components. In some areas, duplicate equipment in the maintenance and logistics sector is avoided, plant monitoring is simplified and the work required to be carried out by the operating staff is facilitated.

[0020] An arrangement of two twin-roll casting devices which likewise reduces or minimizes the length of the tundish results, compared to an arrangement of two twin-roll casting devices positioned next to one another with aligned casting nips, if the two casting nips are arranged parallel and offset with respect to one another in terms of the their longitudinal extents. It is preferable for the production lines which are supplied with metal melt by a common tundish to be arranged so as to lead away from one another.

[0021] The arrangement of the casting nips and/or production lines in accordance with the invention, in particular with angular positions of the production lines with respect to one another of between 45° and 120°, proves particularly advantageous if at least one roll stand is arranged downstream of each twin-roll casting device. On the drive side, rolling stands need space for the drive units of the rolls and on the operating side need space for roll changeover devices. Preferred angular positions of the production lines with respect to one another make it possible to arrange roll changeover stations, the associated bearing equipment and if appropriate also the roll grinding mill in a spatially enclosed area of the production hall between the two rolling stands.

[0022] An efficient casting ladle arrangement is achieved if the casting ladle is supported in a bearing device, if this bearing device is formed by a ladle turntable which can rotate about a vertical axis and has at least two receptacles for casting ladles, and the melt outlet from the casting ladle, in the casting position, is arranged approximately centrally above the tundish, preferably centrally in the region of a projecting limb of a T-shaped tundish. The tundish may also be of trough-like or V-shaped design and can in this way be equated to the T-shaped tundish.

[0023] The metal melt is transferred from the tundish to the twin-roll casting plant in a manner which does not disrupt the formation of strand shells at the casting roll surfaces if the bottom outlets in the tundish comprise submerged casting nozzles which project centrally into a free melt-receiving space between two interacting casting rolls of the twin-roll casting devices.

[0024] For the reasons which have already been described above, the bottom outlets in the tundish are at a distance of no more than 8.5 m apart.

[0025] The invention is described in more detail below on the basis of a plurality of exemplary embodiments which are diagrammatically depicted in the drawings, in which:

[0026]FIG. 1 shows a longitudinal section through a plant for implementing the two-roll casting process in accordance with the prior art,

[0027]FIG. 2a shows a plan view of the plant according to the invention with two production lines arranged at an angle of 90°,

[0028]FIG. 2b defines the angles α and β in the arrangement according to the invention,

[0029]FIG. 3a shows a plan view of this plant with two production lines arranged at an angle of 180°, and

[0030]FIG. 3b diagrammatically depicts a plan view of a variant of the arrangement shown in FIG. 3a.

[0031] An overall plant for producing a steel strip from a steel melt using the twin-roll casting process which has already been described in the introduction, as conventionally used in accordance with the prior art, is diagrammatically depicted in longitudinal section in FIG. 1, which is restricted to the most important components of the plant. Casting ladles 1 filled with steel melt are transferred from the melting works to the casting plant using metallurgical vehicles or a hall crane (not shown) and are then inserted into receptacles 2 of a ladle turntable 4 which can rotate about a vertical axis 3. From the casting ladle 1, which has been moved into the casting position, the steel melt flows through a melt outlet 5 into a tundish 6 and, from this, through a bottom outlet 8 formed by a submerged casting nozzle 7 to the twin-roll casting device 10. The twin-roll casting device 10 is substantially formed by two driven, oppositely rotating casting rolls 11, 12 supported in bearings in a bearing frame (not shown). The casting rolls 11, 12, which are arranged at an adjustable distance with respect to one another, together with side plates arranged at the end sides (not shown in FIG. 1), form a casting nip 13 of limited longitudinal extent and a melt-receiving space 14, in which strand shells which have solidified at the casting roll surfaces are formed; these strand shells are brought together in the casting nip 13 by the rotation of the casting rolls 11, 12 to form a cast metal strip 15. The metal strip 15 is then discharged from the casting nip 13, diverted into the horizontal plane, conveyed onward by pinch roll pairs 16, 17 to a rolling stand 18, where they are held under tension. As the production sequence continues, the metal strip 15 is cooled as it passes through cooling devices 19, transversely divided according to required coil weights by means of shears 20 and wound into coils in a coiler 21. Further devices (not shown), such as a looping pit for compensating for different speeds between individual production devices, trimming shears for treating the edges of the metal strip, evacuation chambers for preventing the formation of scale on the metal strip, reheating devices, etc. are usually integrated in plants of this nature.

[0032] One possible embodiment of an arrangement of two production lines 23, 24 incorporating in each case one twin-roll casting device 10 a, 10 b of the type described above for carrying out the vertical twin-roll casting process is illustrated in FIG. 2a. The two production lines 23, 24 are arranged at an angle β of 90° with respect to one another. The casting nips 13 a, 13 b, which are arranged offset by an angle α of 90° with respect to one another, of the twin-roll casting devices 10 a, 10 b having the casting rolls 11 a, 12 a and 11 b, 12 b are covered by a tundish 6 which extends obliquely across the two twin-roll casting devices 10 a, 10 b and are supplied with metal melt. For this purpose, the bottom outlets 8 a, 8 b are each positioned precisely above the casting nips 13 a, 13 b of the twin-roll casting devices 10 a, 10 b and ensure symmetrical introduction of the metal melt into the melt receiving space 14 (FIG. 1). The ladle turntable 4 has been used to move the casting ladle 1 into a casting position above the tundish 6, in which the metal melt flows into a projecting limb 25 of the T-shaped tundish 6.

[0033] Similar strip treatment devices are arranged in both production lines 23, 24, of which strip treatment devices in each case only a rolling stand 18 a, 18 b for reducing the thickness, improving the microstructure, smoothing the surface etc. of the metal strip and the coilers 21 a, 21 b are illustrated in the diagrammatic representation of FIG. 2a. In addition to the rolling stands 18 a, 18 b, areas for the roll changeover stations 30 a, 30 b and if appropriate further areas (not described in more detail) for the common bearing of roll sets and the roll grinding mill are provided in the area of the hall between the two adjacent production lines 23, 24. The fact that the same strip treatment devices are arranged close together and the possibility of combining them result in favorable working conditions for operating and maintenance staff with short transfer paths and common logistics. Similar synergistic effects result, for example, for the casting roll changeover station and the casting roll workshops, the plant control stand and product logistics.

[0034]FIG. 2b diagrammatically depicts the casting nips 13 a, 13 b of the two casting-roll devices at an angle α of 60°. The angle β between the two production lines 23, 24 is likewise 60°, with the result that the casting nips 13 a, 13 b are always positioned normally with respect to the orientation of the production line 23, 24. Angular positions α and β which differ from one another are also possible but require strip-diverting devices to be arranged in or at the start of the production lines 23, 24.

[0035]FIG. 3a shows a further possible embodiment of an arrangement of two production lines 23, 24 incorporating in each case one twin-roll casting device 10 a, 10 b for carrying out the vertical twin-roll casting process, the casting nips 13 a, 13 b, the twin-roll casting devices 10 a, 10 b and the production lines 23, 24 being arranged at an angle of 180°, i.e. parallel and offset with respect to one another. In this case, the ladle turntable 4 and the tundish 6, starting from which the two production lines 23, 24 are oriented in opposite directions, are in this case positioned in the center of the plant, and accordingly the cast strip passes through the production lines in opposite directions.

[0036]FIG. 3b shows a variant of the plant arrangement illustrated in FIG. 3a, in which the production lines 23, 24 and accordingly also the casting nips 13 a, 13 b and the casting-roll devices are arranged parallel and laterally offset with respect to one another.

[0037] The invention is not restricted to the embodiments illustrated. The individual plant components can be used in various modified forms. It is within the scope of protection of the invention to provide other floor-mounted bearing devices for the casting ladles, such as for example displaceable ladle carriages, instead of the ladle turntable. A casting crane from which the casting ladle is suspended can also be used, replacing the ladle turntable. Depending on the angular positions of the production lines with respect to one another, it is possible to modify the shape of the tundishes, so that they may also be designed as substantially rectangular troughs or as V-shaped tundishes. Modifications to the form of the tundish of this nature are likewise covered by the scope of protection of a T-shaped tundish. A multi-stand rolling device can be used in the individual production lines in order to achieve higher reduction rates. 

1. A plant for producing hot strip from a metal melt in accordance with the twin-roll casting process using two twin-roll casting devices, each of the twin-roll casting devices (10 a, 10 b) being formed by two casting rolls (11 a, 12 a; 11 b, 12 b) which in each case form a casting nip (13 a, 13 b), characterized in that a casting ladle (1) with a melt outlet (5) is assigned a tundish (6) for receiving the metal melt from the casting ladle (1), in that this single tundish (6) is equipped with at least two bottom outlets (8) for transferring the metal melt to two twin-roll casting devices (10), in that each casting nip (13) is assigned at least one of the bottom outlets (8 a, 8 b) of the tundish (6), and the two casting nips (13 a, 13 b) are arranged at an angle α of 15° to 180°, preferably of 45° to 120°, in particular of 60° to 120°, with respect to one another in terms of their longitudinal extents.
 2. The plant as claimed in claim 1, characterized in that the two casting nips (13 a, 13 b) are arranged at an angle α of approximately 90° with respect to one another in terms of their longitudinal extents.
 3. The plant as claimed in claim 1 or 2, characterized in that the production lines (23, 24) which are supplied with metal melt from a common tundish (6) are arranged at a angle β of from 15° to 180°, preferably from 45° to 120°, in particular from 60° to 120°, with respect to one another.
 4. The plant as claimed in claim 3, characterized in that the production lines (23, 24) which are supplied with metal melt from a common tundish (6) are arranged at an angle of approximately 90° with respect to one another.
 5. The plant as claimed in claim 3 or 4, characterized in that the angle α which defines the position of the casting nips (13 a, 13 b) with respect to one another is equal to the angle β which defines the position of the production lines (23, 24) with respect to one another.
 6. The plant as claimed in one of the preceding claims, characterized in that common service areas for at least one, preferably at least two, of the following applications are arranged in the angle region between two adjacent twin-roll casting devices (10 a, 10 b) and the strip treatment devices (production lines) arranged downstream of them: cast-rolling shops, casting roll changeover station, roll change station, roll grinding mills, plant operating stand, product logistics.
 7. A plant for producing hot strip from a metal melt in accordance with the twin-roll casting process using two twin-roll casting devices, each of the twin-roll casting devices (10 a, 10 b) being formed by two casting rolls (11 a, 12 a; 11 b, 12 b) which in each case form a casting nip (13 a, 13 b), characterized in that a casting ladle (1) with a melt outlet (5) is assigned a tundish (6) for receiving the metal melt from the casting ladle (1), in that this single tundish (6) is equipped with at least two bottom outlets (8 a, 8 b) for transferring the metal melt to two twin-roll casting devices (10 a, 10 b), in that each casting nip (13 a, 13 b) is assigned at least one of the bottom outlets (8 a, 8 b) of the tundish (6) and the two casting nips (13 a, 13 b) are arranged parallel and offset with respect to one another in terms of their longitudinal extents.
 8. The plant as claimed in claim 7, characterized in that the production lines (23, 24) which are supplied with metal melt from a common tundish (6) are arranged so as to lead away from one another.
 9. The plant as claimed in one of the preceding claims 1 to 8, characterized in that at least one rolling stand (18 a, 18 b) is arranged downstream of each twin-roll casting device (10 a, 10 b).
 10. The plant as claimed in one of the preceding claims 1 to 9, characterized in that the casting ladle (1) is supported in a bearing device, in that this bearing device is formed by a ladle turntable (4) which can rotate about a vertical axis and has at least two receptacles (2) for casting ladles (1), and the melt outlet (5) from the casting ladle (1), in the casting position, is arranged approximately centrally above the tundish (6), preferably centrally in the region of a projecting limb (25) of a T-shaped tundish (6).
 11. The plant as claimed in one of the preceding claims 1 to 10, characterized in that the bottom outlets (8 a, 8 b) in the tundish (6) comprise submerged casting nozzles (6) which project centrally into a free melt-receiving space (14) between two interacting casting rolls (11 a, 12 a, 11 b, 12 b) of the twin-roll casting devices (10 a, 10 b).
 12. The plant as claimed in one of the preceding claims 1 to 11, characterized in that the bottom outlets (8 a, 8 b) in the tundish (6) are no more than 8.5 m apart. 